This invention relates to a device for detecting and signalling or indicating status as regards contents in a container, and in particular a letterbox. It also relates to a detector-transmitter unit and a receiver-display unit.
A number of devices for detecting and signalling the deposit of mail in a letterbox are known. Common to many of these is that the signalling takes place through the use of visual means arranged on the letterbox, for example, a marker flag or the lighting up of a light source. This means to say that there must be free line of sight from the observer to the letterbox. In blocks of flats where all letterboxes are assembled by the entrance door or, for example, in residential areas where letterboxes are mounted on common stands, this kind of visual signalling to an observer who is not in the immediate vicinity is, as a rule, impossible. In such cases it has therefore been proposed that the signalling should be done via cable networks.
SE Patent 504 819 teaches a letterbox of the type mentioned above which includes detecting or sensing means and indicating means for detecting and signalling the presence of an object in the letterbox. In one embodiment of the letterbox (FIGS. 2 and 3), the detecting means is a light source which directs light towards a photocell that is arranged to control a change-over switch in response to the light beam being broken as a result of the deposit of mail in the letterbox. Although the Swedish device is equipped primarily with a visual indicator on the letterbox itself, it is disclosed that a cable may be used to allow greater freedom in the positioning of the indicator, which, moreover, is also disclosed as being acoustic or of another well-known and conventional type. The SE letterbox has several movable flaps equipped with spring devices and other parts necessary to achieve its purpose. Therefore, it is relatively complicated and costly to manufacture, and to the best of the applicant""s knowledge, it has not been a success. GB 2 078 107 describes a letterbox equipped with a device for signalling the deposit of mail in the letterbox. The device includes, inter alia, a switch arrangement in connection with a flap in the mail insertion slot, and it requires cable transmission to the location at which the mail received signal is given. This system as a whole is thus complicated and calls for a relatively large investment. DE 2 708 286 teaches a letterbox that has a device for detecting and signalling the deposit of contents in the letterbox. When mail is inserted, it is detected by a sensor that activates a remote receiver which is connected to the sensor and which gives visual and/or audible information. This system is especially designed for letterboxes in blocks of flats where, as a rule, these are placed together at the entrance. The document describes a number of alternative sensor embodiments, including the use of a light source where the light from a light-emitting diode falls on a light-sensitive element such as a light-dependent resistor, a photodiode or a phototransistor. Mail deposited in the letterbox breaks the light beams so that the resistance of the light-sensitive element is altered and a signal indicating the deposit of mail is produced. This signal must be relayed to a receiver which, for example, can be installed in the flat, office, etc. belonging to the letterbox owner. It is presumed that this signal transmission will take place via a permanently installed cable network. As an option, it is disclosed that the sensor can be connected to the receiver via a separate electric cable. It is also indicated that such cables should preferably be installed during the construction of the building as later installation would involve considerable costs. However, there is also a discussion of ways of connecting the signal via already existing cable networks such as the doorbell cable network. The signalling then takes place with the use of alternating current or special audible ringing signals are employed. The DE document gives no specific indication of how the device should be made and installed in the letterbox. It seems clear that the DE system will be costly and complicated, and will probably only be justifiable in fairly large communal installations. DE 1 954 531 A1 describes a similar system as that described above, but in this case the main idea is to use the entry phone system for the signalling. Lastly, EP 0 782 117 A1 describes a wireless network for controlling various household units. This network can probably be modified to also monitor letterboxes or the like, but there are no indications of such modifications.
As mentioned, the object of the present invention is to provide a device for detecting and signalling or indicating status as regards contents in a container, and in particular a letterbox, which eliminates the problems of the known devices. It is simple and inexpensive to manufacture, can be easily installed in existing letterboxes or made an integral part of new ones, and requires no cable connection between the detector and signal unit.
This object is achieved with a device for detecting and signalling or indicating status as regards contents in a container, and in particular a letterbox, comprising a detector for registering a change of state in the letterbox, which registration is transmitted to and activates a preferably remote display or the like in order to produce on the display a visual and/or audible message which signals that contents have been deposited in the letterbox, wherein the detector is arranged in a preferably integrated mounting unit made in the form of an approximately U-shaped holder that accommodates a circuit board containing electronic components, a light transmitter, a light receiver, and wires and power supply, which unit is placed on or at the bottom of a container, preferably a letterbox, in such manner that said two upright legs of said holder rest against respective opposite walls of said letterbox, and where light from said transmitter is transmitted through the inner space of said letterbox to said light receiver.
There are preferably provided guide strips on said wall to facilitate the positioning of said unit, and the legs of said holder are preferably elastic to ensure that said unit is held securely in place, and where there may also be provided holes in said holder to enable it be secured to said letterbox by means of suitable fasteners such as screws. The holder may form an integral part of the walls of said letterbox and is made of an appropriate plastic material or another suitable material and is shaped so as to be hollow. One of said upright legs may accommodate a circuit board containing said components, and said light receiver, and said light transmitter may be housed in the other upright leg. Both said light transmitter and said light receiver may however be housed in the same leg and a reflector is placed on the opposite leg. The upper end region of one or both legs is preferably shaped with a bevel edge.
There may be arranged a cover in the bottom of said holder, detachably fastened to said holder, preferably by snap fastening to the bottom edge portions of said holder, and which together with said holder forms a compartment for wires, and there may also be arranged drainage holes in the bottom of the letterbox. The transverse portion of the holder may be made so as to be telescopic.
The invention also comprise a detector-transmitter unit for use in a device for detecting and signalling or indicating status as regards contents in a container, and in particular a letterbox, comprising a detector for registering a change of state in said letterbox. The registration is transmitted to and activates a preferably remote display or the like in order to produce on said display a visual and/or audible message which signals that contents have been deposited in said letterbox. The detector comprises a light emitting diode and a photodiode, or optionally an electronic sensor (inductive/capacitive), an ultrasonic sensor, a mechanical or electromagnetic switch means etc., wherein there is provided an oscillator, a timer to control the timing and a power source, an amplifier, a multivibrator or flip-flop having a first input and a second input and a code circuit having address code inputs and a preferably high-frequency transmitter module. Said timer activates and pulses said detector transmitter component for about 20 milliseconds with a period of about 40 seconds, and if said letterbox or container is empty, said detector receiver component receives pulses from said transmitter component and the response thereto is relayed in the form of electrical signals to said amplifier; and if contents are introduced into said letterbox, the connection between said transmitter component and said receiver component is broken with the result that said amplifier is without a signal. The output from the amplifier is connected to said second input on the multivibrator whose first input is connected to said timer causes said multivibrator to be synchronised at the end of the activation time of said transmitter component, and the logical state of said flip-flop thus becomes a signal which indicates whether there are contents in said letterbox or not, the activation time and the period being implemented by a circuit with the oscillator at fixed frequency and counter elements which, depending on the number of elements and their connection, indicate the time intervals, and where the voltage from said oscillator is preferably used to operate the power source of said transmitter component, and the information from said flip-flop is passed to said code circuit which codes this information together with an address signal in the form of a serial telegram that controls said high-frequency transmitter which transmits the address and data or information telegram immediately after the activation time for said transmitter component when the contents of said letterbox has been detected.
Further, the invention comprise a receiver-display unit for use in a device for detecting and signalling or indicating status as regards contents in a container, and in particular a letterbox, comprising a detector for registering a change of state in said letterbox, which registration is transmitted to and activates a preferably remote display or the like in order to produce on said display a visual and/or audible message which signals that contents have been deposited in said letterbox, which detector comprises a light-emitting diode and a photodiode, or optionally an electronic sensor (inductive/capacitive), an ultrasonic sensor, a mechanical or electromagnetic switch means etc. Said receiver and display unit comprises a preferably high-frequency receiver, a decoder, a monostable multivibrator or flip-flop and a display, where said display comprises a visual and/or audible signal means, and where said telegram on reaching said receiver is passed to said decoder that ascertains whether said telegram contains a valid receiver address and determines the logical state of the data or information; if the information indicates that there are contents in said letterbox, an appropriate signalling means on said display is activated.
Advantageous embodiments of the invention are disclosed in the dependent patent claims.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof.